Consolidate documentation (#3071)

* 🔥 consolidate documentation
* ♻️ overwork std specializations
* 🚚 move images files to mkdocs
* ♻️ fix URLs
* 🔧 tweak MkDocs configuration
* 🔧 add namespaces
* 📝 document deprecations
* 📝 document documentation generation
* 🚸 improve search
* 🚸 add examples
* 🚧 start adding documentation for macros
* 📝 add note for https://github.com/nlohmann/json/issues/874#issuecomment-1001699139
* 📝 overwork example handling
* 📝 fix Markdown tables

doc/mkdocs/docs/api/json_pointer/parent_pointer.md

@@ -0,0 +1,35 @@
+# <small>nlohmann::json_pointer::</small>parent_pointer
+
+```cpp
+json_pointer parent_pointer() const;
+```
+
+Returns the parent of this JSON pointer.
+
+## Return value
+
+Parent of this JSON pointer; in case this JSON pointer is the root, the root itself is returned.
+
+## Complexity
+
+Linear in the length of the JSON pointer.
+
+## Examples
+
+??? example
+
+    The example shows the result of `parent_pointer` for different JSON Pointers.
+     
+    ```cpp
+    --8<-- "examples/json_pointer__parent_pointer.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/json_pointer__parent_pointer.output"
+    ```
+
+## Version history
+
+Added in version 3.6.0.